Joty—An Estimate of the Geological Age of the Earth. 47 
The mass of 64 x 10" tons contains 940 x 10% tons of Na,O. Adding the 
amount in the ocean (21 x 10” tons), we obtain 30°4 x 10” tons. This restored to 
the original mass of 91 x 10" tons gives a percentage of 3°34. 
It may be independently shown that the soda ratio of the original rock to that 
of the sedimentaries supports the view that 30 per cent. must have been about the 
loss, by solution, of the original rock. We assume that the sedimentaries are 
derived from an original rock, such as Clarke arrived at, but we assume no more. 
To see this, we have to refer again to Mr. Merrill’s valuable book,* which gives 
a useful collection of analyses of rocks and their derived soils. 
Omitting afew cases, 7. ¢e. a Phonolite containing a soda-zeolite giving excep- 
tional results on weathering, an incompletely recorded Basalt, and a Soapstone, 
his examples give the following results :— 
Percentage loss of Percentage of each constituent lost. 
entire rock 
revealed in the 
residual soil. NasO K.0 
Granite (p. 209), . 5 13°47 28°62 31:98 
Gneiss (p. 215), . : 44:67 95°08 85°52, 
Syenite (p. 216), . . 56°28 97-11 81°85 
Diabase (p. 221), . : 14:93 12°83 29°15 
59 (do PR), og : 39°51 95°37 45°88 
Basalt (p. 223), . : 60°12 74:41 83°34 
Diorite (p. 225), . é 87°51 84°87 38°75 
Mean, . : 38°6 69°7 56°83 
This indicates that, if at this stage of weathering, these soils were removed, 
redeposited, and reconsolidated, the mass of the parent rock would have been 
correctly estimated, on the basis that the mass removed in solution formed but 
thirty-eight per cent. of the original rock. At this stage of weathering we see 
that 69:7 per cent. of the original soda was removed. 
If we assume that the loss of the soda bears to the loss of the entire rock a 
constant ratio—and with the exception of the first quoted Diabase this appears 
supported by the individual examples—we can apply to the mean analysis of the 
sedimentaries on the one hand, and to that of the mean original crust on the other, 
to arrive at a rough estimate of the loss of entire rock by solution in the process 
of formation of the former. 
We find that (ante) 3°61 per cent. of Na,O in the crust is represented by 1:47 
per cent. in the sediment. From these figures we can calculate the amounts of 
this constituent lost and saved. ‘To effect this accurately we must suppose some 
* << Treatise on Rocks, Rock Weathering, and Soils.”” Macmillan, 1897. 
TRANS, ROY. DUB. SOC., N.S. VOL. VII., PART II, I 
